Locking means and ground connection for electrical plugs



April 1954 H. HUBBELL ET AL LOCKING MEANS AND GROUNDYCONNECTION FOR ELECTRICAL PLUGS 4 Filed March 5. 1950 3 8 Z 6 i, 5 1 3 4 If r an WI-fw a 1% W 9/0 $4 My w x Z L F nu 3 l 2 7 4 d M :W 3 5 d v mentors Patented Apr. 6, 1954 LOCKING MEANS AND GROUND CONNEC- TION FOR ELECTRICAL PLUGS Harvey Hubbell, Long Hill, and Joseph F. Healy, Westport, Conn., assignors to Harvey Hubbell, Incorporated, Bridgeport, Conn., a corporation of Connecticut Application March 3, 1950, Serial No. 147,362

3 Claims. 1

construction which avoids any exposure of live parts on the exterior either of the plug or the associated receptacle, so that there is no danger of any such parts being touched by anyone.

One specific aspect of the invention relates to locking devices for plugs used with three conductor cables which frequently are provided with 1 metallic sheaths, and a further object is to provide a locking device constructed and arranged to form part of the grounding connection be tween the neutral contact blade of the plug and the metallic cable sheath, thereby grounding the locking mechanism and eliminating the possibility of exposed live parts on the plug.

With the foregoing and other objects in view, we have devised the construction illustrated in the accompanying drawing forming a part of this specification. It is, however, to be understood the invention is not limited to the specific details of construction and arrangement shown, but may embody various changes and modifications within the scope of the invention.

In this drawing:

Fig. 1 is an end elevation showing the interior of a plug having a locking mechanism constructed in accordance with one embodiment of this invention;

Fig. 2 is a side view partly in elevation and partly in section on the line 22 of Fig. 1, showing the plug operatively mounted in a connecting receptacle;

Fig. 3 is a transverse section on the line 3-3 of Fig. 1;

Fig. 4 is a section of a plug contact blade which also forms a cooperating part of the locking mechanism;

Fig. 5 is an elevation partly in section of the blade shown in Fig. 4, and

Fig. 6 is an end view looking from the bottom of Figs. 2 and 3, showing an associated cable in section.

The present invention contemplates a locking device forming a permanent part of the connector plug, so arranged as to be easily operated. from the outside of the plug while, at the same time, avoiding any possibility of an operator or anyone else having to touch a live part.

The illustrated embodiment of the invention is shown in connection with a plug I I having a metallic sheath or cover 12 adapted to be secured to the metallic sheath I3 of a cable I4 by a clamp I5 having cable gripping jaws I6 and radial flanges I'l secured between the plug sheath or cover I2 and the main insulating body I8 of the plug. The clamp projects through the axial opening I9 in the sheath or cover of the plug. Each cable gripping jaw has cars 20 engaged by clamping screws 2| for securing the clamp to the cable sheath I3. The feet slide laterally in grooves Ila on the inner side of the end wall of the cover or shell.

As illustrated, the cable I4 is a three conductor cable having two live conductors 22, 23 and a neutral conductor 24. The former are connected to contact blades 25, 26 respectively, by means of the usual binding screws 25a. The neutral conductor 24 is connected to a grounding blade 21 of u-shaped cross section as shown in Figs. 1, 4. and 5, by a binding screw 210, on base plate 28 mounting the blade 21.

In the present invention the locking mechanism is so connected to the neutral or grounded conductor that all possibility of any exposed live part is entirely eliminated. This mechanism is shownas including a locking member in the form of an elongated screw threaded bolt or screw 3| extending through an opening 32 in the plug body I8 at an acute angle to the axis of the plug. The screw 3! extends through and is threaded to the U-shaped grounded contact blade 21, so that it can be readily screwed into and out of the locking position, in which position its inner end am engages a part of the insulating material 34 of associated receptacle 33 in which the plug is mounted. As shown, the screw is threaded to both the base 28 and the projecting body portion 29 of the U-shaped grounded blade 21, suitable threaded or tapped openings 34a and 35a being formed in the blade for that purpose, and they are inclined so that the screw is at an angle to the axis of the plug for a purpose presently to be described.

The receptacle 33 has the usual openings and blade receiving contacts for connection to the blades of the plug upon insertion of the plug therein. These include contacts 33a for engagement with contact blades 25 and 2B and a contact 36 in chamber 38a for receiving the U- shaped grounded blade on the plug ll, and which is connected through a binding screw 3'1 with the neutral conductor 38 of the three conductor cable 39.

'As shown in Figs. 2 and 6, the locking screw 3! extends through an opening in an ear 4| struck up from the metallic casing I2 of the plug body II to form a ground connection from the blade 21 to the cable sheath I3, and also a support for the outer. portion of .the screw,.in addition to the conventional ground connection for the blade shown at 43 secured to base 28 by the mounting rivet 44 and extending at its outer end 45 under and into engagement with metal shell l2. The end of the screw 3| has a knurledandslotted head 42 to facilitate the operation'thereof into and out of operative position.

Before inserting the plug into the receptacle 33 the locking device is retracted into inoperative position. In the illustrated embodiment. this requires unscrewing the threaded bolt or screw 3| until the outer end 31a is retracted within the plane of the contact 21 so that it doe not project outwardly far enough to interfere with inserting the plug in the receptacle.

contact 36 is mounted. In this position the screw threads cut into thematerial of the body'of the receptacle and lockthe plug against withdrawal from the receptacle, while'release of the :thereon including a portionprojecting from the body for'insertion in a slot in 'a' receptacle leading to a recess containing a contactforengagement thereby, a screw extending through the body of the plug and inclinedto'the axis of the plug, andsaid screw being threaded into the projecting portion or the .contactblade and including an inner end-projectable from one side of this blade so that inward adjustment of the screw relative. to the, plug will cause its inner end to engage and grip a side wall oftherecess to retain the, plug in the receptacle.

After the plug is'in placesinthe receptaclathe screw3i is screwed into the plug until'the innerend 3l"a of this screw engages the adjacent surface 34 of the plug slot 35in which the blade receiving 2. An electrical plug comprising a body of insulating material and a contact blade mounted thereon including a portion projecting from the bod for insertion in a slot in a receptacle leading toa recess containing a contact for engagement thereby, ametallic sheath forsaid body, a screw grounded on the sheath extending through the body of the plug and inclined to the axis of the plug, said screw being threaded into the projecting portion of 'the contact blade so as to ground the contact blade on the sheath and including an inner end projectable from one side of this blade sothat inward adjustment of the screw relative to the plug will cause its inner end to engage and grip a side wall of the recess to retain the plug in the receptacle.

3. An electrical plug comprising a body of insulating material and a contact blade mounted thereon including a portion projecting from the body for insertion in a slotin a receptacle leading to arecess containing a contact'for engagementthereby, a'metallic cover for the body including means forgrounding it on the metalcovering of a conductorcable, a screw threaded in the projecting portion of said blade and inclined to the axis of the plug, said screw extending through the body and cover and grounded on'said cover to ground the contactblade thereon and including an inner end projectable i'rom onesi'de of this blade, and said screwbeing adjustable from the exterior of the cover to cause its inner end to engage and grip a side wall 01 'thcrecess to retain the plug in the receptacle.

ReferencesCited in the file or this patent UNITED STATES PATENTS Number Name Date 1,144,225 Mills June 22,1915 1,509,839 Kuhn LSept.,30, 1924 1,782,527 Bennett Nov. 25,- 1930 1,891,153 Gates Dec. 513,.1932 1,967,021 Gary :July 17,1934 2,049,093 Thorin .:Ju1y-28,' 1936 2,410,618 Zelov -Nov.-6, 1946 

